I think Bryan Caplan's latest post on kids and happiness suggests a better angle for his project:
I looked at this question using the GSS, regressing happiness on marital status, job satisfaction, real income, a personality measure (“You sometimes can't help wondering whether anything is worthwhile any more.”), and number of children. Children have the standard negative effect, and it's statistically significant, too. But the size is miniscule. Each child brings you down by .015 steps on a 3-point happiness scale.
In contrast, just being married gives you a boost of .286. If you take the linear model literally, that means that a married person would need 19 kids to have the expected happiness of a childless single! Of course, the linear model is pretty silly, but it does put the standard finding in perspective. The average effect of children on happiness is very tiny.
Now consider: In the real world, a very small average effect probably means that some people hate having kids, while others love the experience. So before you decide that you're too selfish to accept even a small reduction in your personal happiness, you might want to find out the best ways to beat the average. …
Let me just say that, yes, the simple model is pretty silly. The famous-for-happiness-research panel study by Diener, Lucas et al. found that “on average, people adapt quickly and completely to marriage.” (But see Zimmerman and Easterlin [pdf], who are skeptics, like me, of the strong setpoint-adaptation theory.) So Bryan wouldn't want to make his comparison in quite this way. But Diener et al also found a good deal of individual-level variance. Some people were much better off right after marriage and never completely adapted. Some people were much worse off after marriage and never completely adapted. So the question you want to know is: which kind of person are you?
No doubt people respond differently to children as well. So Bryan and his readers would be well served by exploring what kind of people are most and least likely to take a happiness hit from breeding, exploring the reasons kids cut into happiness for most people, and examining strategies for, as he says, beating the average. That is, his angle ought to be: You can do things to make having kids not as bad as it usually is. Instead of: Kids make you happier than you may recognize. Because what people don't recognize is not that kids are a joy, but that they are more likely than not to make you less happy.